An electric double-layer capacitor, also known as a “supercapacitor,” “supercondenser,” “pseudocapacitor,” “electrochemical double layer capacitor” (EDLC),” or “ultracapacitor,” (hereinafter referred to as an “EDLC”) is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors. EDLCs can have long cycle life and fast recharging times suitable to provide sufficient power demanded for heavy-duty electronics and electric vehicles. Multiple power applications favorably harness the high power of EDLCs instead of batteries with lower power output.
In a battery, solid-state Faradaic processes often lead to poor cycling reversibility and limited power performance. EDLCs are based upon the electrochemical double layer phenomenon at the interface between a polarized electrode and a liquid electrolyte. An EDLC can include two electrochemical double layers linked in series by an electrolyte bridge. Operation of EDLCs can involve neither inter-electrode mass transfer nor solid-state ion diffusion, which can lead to long cycling life and high-power.
Significant progress has been made to EDLCs in terms of power densities and physical flexibility. Unfortunately, the low energy densities of current EDLCs, generally about <5 Watt hour per kilogram (Wh/kg), seriously limit the applications of the EDLC.